Turkish President Recep Tayyip Erdoğan said Thursday that the treaty defining border relations between Greece and Turkey should be trashed, the Guardian reported.

In the first official visit to Greece by a Turkish head of state in 65 years, Erdoğan reportedly stoked tensions by disparaging the Lausanne Treaty, which defines boundaries between the two countries and the border between EU member Greece and non-member Turkey.

The Turkish president cited treatment of Muslims in Greece as evidence that the treaty is not being implemented fairly, to which Greek President Prokopis Pavlopoulos responded that the treaty “is non-negotiable,” and “has no flaws, it does not need to be reviewed, or updated.”

During a tense back-and-forth between the two sides, Erdoğan also said Greece’s admittance to NATO was thanks to Turkey’s support.

Greek Prime Minister Alexis Tsipras later tweeted that his government is committed to maintaining the “Greek-Turkish friendship” which must be based on “respect for international treaties.”